We reviewed six free flap reconstructions of the weight-bearing surface of the heel. Patients were seen for clinical evaluation at a mean follow-up of 4.7 years (range 2.7-6.0 years). Functional results using a modified Boston Children's Hospital Ankle Score were 33% excellent, 33% good, 17% fair, and 17% poor. The excellent functional results were related to the absence of chronic draining flap ulcers. All flaps lacked protective sensation by Semmes-Weinstein monofilament testing. Weightbearing plantar pressures in the flaps were elevated in all patients. Sequential radiographs from the time of flap coverage revealed the development of a bony protuberance (stalactite) projecting from the undersurface of the calcaneus in all patients with injuries to the plantar cortex of the calcaneus. In patients with flap ulceration, these stalactites projected into the ulcer at the site of maximum plantar pressure. A combination of loss of plantar calcaneal integrity, elevated pressure concentrations, and flap insensitivity appear causally related to the development of heel free flap ulceration and outcome.